The overall project concerns the role of coagulation proteins in platelet function and the various interactions between platelets and coagulation proteins. The proposed work is intended to investigate interactions of platelets, fibrinogen and thrombin with regard to 1) the adsorption of exogenous fibrinogen on platelet surfaces and isolated platelet membranes, 2) the conversion of adsorbed fibrinogen to fibrin at the surface of intact platelets, and 3) the function of released endogenous platelet fibrinogen and its interaction with adsorbed surface proteins. BIBLIOGRAPHIC REFERENCES: Watanabe, K., Chao, F.C., and Tullis, J.L.: Platelet antithrombins: Role of thrombin binding and the release of platelet fibrinogen. Br. J. Haematol. 35:119, 1977. Lawler, J.W., Chao, F.C., and Fang, P.H.: Observation of a high molecular weight protein released by thrombin. Thrombos. Haemostas. (Stuttg.), in press, 1977.